1. Field of the Invention
The present invention relates to a thin-film transistor substrate obtained by forming thin-film transistors (TFTs) on an insulating substrate, a display device formed by combining the thin-film transistor substrate and a display material such as a liquid crystal material and an EL material, and a CAD for designing the thin-film transistor substrate and the display device. The present invention also relates to a transfer method for the thin-film transistor substrate, which prevents breakage of wiring lines caused by static electricity.
2. Description of the Related Art
FIG. 1 shows a structure of a crystal display device and a schematic circuit diagram of a thin-film transistor substrate used for the display device. In a pixel region 1, pixels (display dots) 2 are arranged in a matrix. In each pixel 2, a pixel electrode 3, a storage capacitor 4, and a pixel transistor 5 are arranged. The pixel electrode 3 and a counter electrode 6 (in practice, a large electrode provided throughout the whole pixel region 1) sandwich liquid crystal 7 therebetween.
Each pixel transistor (thin-film transistor) 5 is connected to a gate electrode line (scan line) 8 and an image signal line 9, and each storage capacitor 4 is connected to a common capacitor line 10. The gate electrode lines 8 are connected to a gate line driving circuit 11, the image signal lines 9 are connected to a signal line driving circuit 12, and the common capacitor lines 10 are connected to a capacitor line driving circuit 13 (for example, see Japanese Patent Laid-Open Publication No. 2000-187248).
Other various components including a system circuit and a polarizer, as well as a backlight are further added to and combined with the structure shown in FIG. 1, completing a liquid crystal display device. In this structure, the pixel electrodes 3, the storage capacitors 4, the pixel transistors 5, the gate electrode lines (scan lines) 8, the image signal lines 9, and the common capacitor lines 10 are formed on an insulating substrate, configuring a thin-film transistor substrate.
With regard to a thin-film transistor substrate where polysilicon (Si) is used for thin-film transistors, the gate line driving circuit 11, the signal line driving circuit 12, and the capacitor line driving circuit 13 may be formed on the same insulating substrate.
FIGS. 2A and 2B are schematic views of the half-manufactured liquid crystal display device shown in FIG. 1 and depict four pixels formed in the pixel region on the thin-film transistor substrate. FIG. 2A is a schematic plan view of the same and FIG. 2B is a schematic cross-sectional view taken along the line α-β in FIG. 2A.
As shown in FIG. 2A, each gate electrode line 8 intersects with a plurality of semiconductor layer patterns 20. The common capacitor lines 10 are formed parallel to the gate electrode line 8. Quadrangles drawn by a dotted line represent positions where the image signal lines 9 are to be formed.
As shown in FIG. 2B, an undercoat film 22 is formed on an insulating substrate 21, and the semiconductor layer patterns 20 and a gate insulator 23 are formed on the undercoat film 22. The gate electrode lines 8 are then formed on the gate insulator 23, and an interlayer insulator 24 is formed on the gate electrode lines 8.
Such display device (a liquid crystal display device) as shown in FIGS. 1 and 2, where each display pixel has a thin-film transistor, requires an enormous number of pixels to display a large amount of data. In the case of a typical screen (for example, 1024*768 pixels) of a personal computer, where the RGB colors are made of three pixels (i.e. one pixel forms one color) there will be as many as several millions of pixels that need to be formed. As the demand for display quality has been increasing every year, the demand for display devices having the fewest possible (minimum) point defects due to pixel failures has also been on the rise. However, at manufacturing sites, it is very difficult to fabricate display devices having no point defects at all with good yield, and it is thus very important to provide display device structures with a fewest possible point defects and a manufacturing method for such display devices.
One of significant causes of point defect is electro static discharge which occurs when forming a thin-film transistor substrate. In particular, during a period between formation of the gate electrode lines 8 and formation of the image signal lines on a top-gate-type thin-film transistor substrate, high voltage is likely to be generated between each substrate layer pattern 20 and each gate electrode line 8, and electro static discharge is also likely to occur during the period. Deposition and washing processes after formation of the gate electrode lines 8 as well as transfer (movement of substrates) in these processes are of particular problems.
FIGS. 3A and 3B are schematic explanatory views showing a deposition process for the interlayer insulator after formation of the gate electrode lines, and electro static discharge that occurs while the substrate is being transferred, respectively. FIG. 3A shows a state within a plasma CVD chamber 25 where the semiconductor layer patterns (polysilicon) 20 and the gate electrode line 8 are formed on the substrate 20 together with the undercoat film and gate insulator, and an insulator (for example, silicon oxide or silicon nitride) is adhered onto the gate electrode line 8 by plasma CVD as the interlayer insulator 24. In this state, the entire substrate is charged. Since the substrate and its surface (the interlayer insulator) are made of an insulating material, complete static elimination is difficult.
FIG. 3B is a schematic explanatory view of electro static discharge during transfer of the substrate. During transfer of the substrate 21 from the state shown in FIG. 3A, once the semiconductor layer pattern 20 comes to a position above a substrate support portion 40 of an arm of a substrate transfer robot, electro static discharge (depicted symbolically) often occurs in the semiconductor layer pattern 20.
An object of the present invention is to provide a thin-film transistor substrate which can suppress point defect caused by such electro static discharge, improving manufacturing yield.